(1) Field of the Invention
The present invention relates to a brushless self-excited synchronous generator, and more particularly to a three-phase self-excited synchronous generator which is simple and rigid in its structure, in which magnetic vibrations and noise are reduced, which is capable of producing voltages of flat-compound characteristics against load variations due to the provision of a series excitation function internally, and in which the output voltages respectively at non-loaded and loaded states are freely controllable.
(2) Description of the Related Art
A brushless self-excited synchronous generator which has a series excitation function internally and which is capable of outputting a voltage of flat-compound characteristics is disclosed in, for example, Japanese Patent Application Kokai Publication No. Hei 3-245755 or Kokai Publication No. Hei 4-285454. FIG. 1 diagrammatically shows a circuit of such a brushless self-excited synchronous generator disclosed in the former Publication No. Hei 3-245755 and FIG. 2 diagrammatically shows a circuit of the same disclosed in the latter Publication No. Hei 4-285454.
Referring to FIG. 1, an explanation is made on the brushless self-excited synchronous generator disclosed in Japanese Patent Application Kokai Publication No. Hei 3-245755. On a stator iron core 20, there are wound primary generating windings U, V, W of two poles (in this embodiment) having a concentrated full-pitch or its corresponding winding structure, and stator field windings 21 having the number of poles five times (in this embodiment) that of the primary generating windings, that is, ten poles (in this embodiment). On a rotor iron core 22, there are wound rotor field windings 23 which have the same number of poles as that of the primary generating windings, that is, two poles (in this embodiment) and rotor excitation windings 24 which have the same number of poles as that of the stator field windings 21, that is, ten poles and which are magnetically coupled with fifth-order spatial higher harmonic components (ten-poles magnetic fields) of the armature reaction magnetic fields produced by the currents in the primary generating windings. Center tap terminals u, v, w, respectively, provided on the phase primary generating windings U, V, W are connected to the stator field windings 21 through a control rectifier device VR which is formed by a three-phase full-wave rectifier 25 and a variable resistor R.sub.f. The rotor excitation windings 24 are connected to the rotor field windings 23 through a diode bridge circuit 26.
Now, actual operation of the above brushless self-excited generator is explained. When the rotor is rotated, electromotive forces are induced in the primary generating windings U, V, W due to the residual magnetism in the rotor iron core 22. Alternating currents (AC) flow in the primary generating windings U, V, W dependent on the induced electromotive forces. The induced electromotive forces are also applied, after having been rectified by the three-phase full-wave rectifier 25, to the stator field windings 21 so that a direct current (DC) I.sub.fs flows in the stator field windings 21. In the rotor excitation windings 24, there are induced overlapped electromotive forces the magnitude of which depends on the static magnetic field produced by the DC current I.sub.fs flowing in the stator field windings 21 and those based on the fifth-order harmonic components of the armature reaction magnetic field produced by the AC currents flowing in the primary generating windings. The overlapped electromotive forces thus induced are rectified by the diode bridge circuit 25 so that a direct current I.sub.f flows in the rotor field windings 23. As a result, the primary magnetic fields increase and the electromotive forces induced in the primary generating windings increase accordingly. The value of the output voltage is self-established based on the repetition of the operation explained above. In the case where the residual magnetism in the rotor iron core 22 is insufficient, a starting or initial excitation may be carried out by a battery B directly connected to the stator field windings 21.
In the above brushless self-excited synchronous generator, in accordance with the increase or decrease in the three-phase resistor loads or inductive loads (lagging power factor), the fifth-order spatial higher harmonic components of the armature reaction magnetic fields increase or decrease in proportion to the increase or decrease in the load currents and, as a result, the DC currents I.sub.f in the rotor field windings 23 increase or decrease, whereby the fluctuations of the output voltages are prevented. Thus, the generator can produce an output voltage of the flat-compound characteristics with respect to the increase or decrease in the loads. In the case where three-phase unbalanced loads or single-phase loads are applied to the above generator, though the series excitation effects due to the fifth-order spatial higher harmonic components of the armature reaction magnetic fields will be lowered as compared with the case of the three-phase balanced loads, electromotive forces are induced in the rotor field windings 23 by the spatial fundamental component of opposite phase of the armature reaction magnetic fields at the three-phase unbalanced loads or the single-phase loads. Since the induced electromotive forces are rectified by the diode bridge circuit 26 and compensate the reduced amount of the DC current I.sub.f in the rotor field windings 23, which is caused by the decrease of the series excitation effects, the generator at the three-phase unbalanced or single-phase load state exhibits the same flat-compound characteristic as in the three-phase balanced load state. Further, with the above brushless self-excited generator, the output voltages respectively at the non-loaded and loaded states can be freely controlled by the control of the DC variable resistor R.sub.f serially connected to the stator field windings 21.
The brushless self-excited synchronous generator disclosed in Japanese Patent Application Kokai Publication No. Hei 4-285454 has the following circuit structure. Armature windings U, V, W of two poles (in this embodiment) having a concentrated full-pitch or its corresponding winding structure are wound on a stator iron core 27. A reactor 28 is connected in parallel to the armature windings U, V, W, thereby forming closed loop circuits. On a rotor iron core 29, there are wound rotor excitation windings 30 of ten poles (in this embodiment) which are magnetically coupled with the fifth-order spatial higher harmonic components of the armature reaction magnetic fields produced by the armature windings U, V, W, and rotor field windings 31 which have the same number of poles as that of the armature windings, that is, two poles in this embodiment, which are supplied with the electromotive forces induced in the rotor excitation windings 30 after having been rectified or converted into DC currents. A rectifier 32 for converting the electromotive forces induced in the rotor excitation windings 30 into the DC currents is provided on the rotor iron core 29.
Now, actual operation of the above brushless self-excited synchronous generator is explained hereinafter. Where the rotor is rotated, electromotive forces are induced in the armature windings U, V, W due to the residual magnetism in the rotor iron core 29, so that reactor excitation currents flow in the armature windings and the reactor 28. The fifth-order spatial higher harmonic components of the armature reaction magnetic fields produced by the excitation currents cause the electromotive forces to be induced in the rotor excitation windings 30, and the induced electromotive forces are full-wave rectified by the rectifier 32 connected between the rotor excitation windings 30 and the rotor field windings 31. Consequently, DC currents flow in the rotor field windings 31, whereby the primary magnetic fields increase and the electromotive forces induced in the armature windings increase accordingly. The value of the output voltage is self-established based on the repetition of the above operations. If a variable type reactor is adopted as the reactor 28, the output voltage at the non-loaded state can be freely controlled by the controlling of the reactor excitation currents.
In the case where three-phase loads are loaded to the generator, vector sum currents of the load currents and reactor excitation currents flow in the armature windings U, V, W. Therefore, due to the effects of the reactor, even if the load currents are constant, the amount of currents (armature currents) to flow in the armature windings increases as the lagging degree of the power factor of the loads increases, and the same decreases as the leading degree of the power factor of the loads decreases. As a result, in this generator, in accordance with the advancement of the lagging degree of the load power factor, the series excitation effects of the field system increase whereby the lowering of the output voltage is prevented. On the other hand, in accordance with the advancement of the leading degree of the load power factor, the series excitation effects of the field system decrease whereby the rising of the output voltage based on the self-excitation phenomena by the phase-advancing currents is prevented. That is to say, the above generator internally possesses an automatic voltage control function capable of appropriately responding to the variations in the power factor of the loads. Further, in the case where three-phase unbalanced loads or single-phase loads are loaded to the generator, the generator operates in the same way as in the case of the three-phase balanced loads except that the spatial fundamental component of an opposite phase of the armature reaction magnetic fields add to the series excitation effects of the field system.
However, the brushless self-excited synchronous generators disclosed in Japanese Patent Application Kokai Publication Nos. Hei 3-245755 and Hei 4-285454, respectively, have the following problems.
There has been a common problem in both the generators disclosed in the above publications that two kinds of windings, that is, rotor field windings and rotor excitation windings need be wound on a rotor iron core. The need for a plurality of kinds of windings to be wound on the rotor iron core inevitably makes the rotor structure complex. Further, the mechanical strength of the rotor is lowered. Moreover, the possibility that such accident as short-circuiting or burning caused by the deterioration of insulation becomes high. Therefore, it is desirable that windings of a single kind be wound on the rotor iron core for the purpose of enhancing rigidity and reliability of the generator.
Further, since the brushless self-excited synchronous generator disclosed in the above Japanese Publication No. Hei 3-245755 adopts a method wherein the series excitation effects are obtained by using a specific order harmonic component among the spatial higher harmonic components of the armature reaction magnetic fields produced by the primary generating windings, the number of poles of the rotor excitation windings which are magnetically coupled with the spatial higher harmonic component of the specific order and that of the stator field windings which are magnetically coupled with the rotor excitation windings must be the same number as the number of poles of the specific order harmonic component. For example, in the three-phase two-pole generator, where the fifth-order spatial higher harmonic component of the armature reaction magnetic fields is used as the series excitation effects, the number of poles of both the stator field windings and the rotor excitation windings is required to be ten (10) poles, while in the three-phase four-pole generator, it is required to be twenty (20) poles. For this reason, the number of slots of the stator core and the rotor core on which the above windings are wound is limited to a certain specific number according to the specific order of the spatial higher harmonic components used for the series excitation effects of the field system.
Specifically, in the above three-phase two-pole generator, the number of slots in the stator iron core is specified to 30 n (n being a positive integer) with winding of the primary generating windings on the stator core being taken into consideration, and the number of slots in the rotor iron core is specified to 10 m (m being a positive integer) with winding of the field windings on the rotor core being taken into consideration. In the three-phase four-pole generator, the number of slots in the stator core is specified to 60 n (n being a positive integer) and the number of slots in the rotor core is specified to 20 m (m being a positive integer). The number of slots in both the cores are assumed that slots are provided with regular intervals on the peripheries of the respective cores.
In the case where the number of slots in each of the stator and rotor cores must be limited to a specific number as above, there arises the following problem. In a rotary machine, there is a possibility that a large amount of magnetic vibrations or noise occur depending on some combinations of the number of slots in the stator core and the number of slots in the rotor core. Therefore, in the rotary machines, generally, the combination of the number of slots in each of the stator and rotor cores is so selected that the magnetic vibrations and noise become small. However, in the above explained brushless self-excited synchronous generator, since the number of slots in each of the stator and rotor cores is limited to a certain specific number which is determined by the selected order of the harmonic components, it is not possible to freely select the combination of the numbers of slots for the purpose of reducing the magnetic vibrations and noise. As a result, there has been a possibility that a great amount of magnetic vibrations and noise occur depending on the combination of the slot numbers which are determined by the specific order used of the spatial higher harmonic components.
Further, since the brushless self-excited synchronous generator also adopts a method wherein the series excitation effects are obtained by using the harmonic component of a specific order among the spatial higher harmonic components of the armature reaction magnetic fields produced by the primary generating windings, the rotor excitation windings magnetically coupled with the specific order spatial higher harmonic component are mounted on the rotor, thereby specifying the number of slots in the rotor iron core. Therefore, the selection range in the combinations of the numbers of slots in each of the stator and rotor cores is small. The generator has the same problem that the magnetic vibrations and noise occur as in the generator disclosed in Japanese Patent Application Kokai Publication No. Hei 3-245755.